The Khrunichev Proton rocket's planned return-to-flight launch, scheduled for 15 September, has been postponed for unspecified "technical reasons". The launch has not yet been rescheduled.
A problem was discovered with the first stage of the vehicle, which houses its six Energomash RD-253 engines, according to International Launch Services (ILS), which markets the rocket.
"It was determined that further investigation is necessary, requiring the launch vehicle be returned to the processing hall for additional testing. The vehicle and satellite remain in a safe configuration at the launch site," says the statement.
The mission is to be the 388th launch attempt for the vehicle, lofting the Astra-2E communications satellite.
Further details are unavailable, and neither ILS nor Khrunichev responded to immediate questions.
Proton was grounded following a 2 July mishap during a Russian government mission, when the rocket crashed immediately after lift-off. The crash was traced to an incorrectly installed angular sensor.